Thermoplastic orthopedic brace and method of manufacturing same

ABSTRACT

Thermoplastic, thermoshapable composite laminate bars, an orthopedic brace using the shaped composite bars as integral components, and a method of thermoshaping the composite bars for use as fitted components in the orthopedic brace are provided. The composite bars contain multiple fiber layers oriented in at least two directions with respect to the bar length to provide high flexural and torsional strength. The novel method of thermoshaping yields improved results over prior thermoshaping methods by providing an uncomplicated shaping capability while maintaining the structural and mechanical properties of the composite bar.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional application of application Ser. No. 08/332,976,filed Nov. 1, 1994 now U.S. Pat. No. 5,624,386, which in turn is acontinuation-in-part of the parent application Ser. No. 08/196,925,filed Feb. 15, 1994, now U.S. Pat. No. 5,529,826.

FIELD OF THE INVENTION

This invention relates to thermoplastic composite materials that areused as structural elements, and more particularly, to the use ofthermoplastic composite materials as components for orthopedic bracingdevices, and methods for manufacturing such components.

BACKGROUND OF THE INVENTION

The key elements of a traditional knee-brace or elbow-brace orthosisconsist of two pairs of upright bars connected to a pair of hingescentered at the appendage joint; the respective pair of bars extendabove and below the appendage joint to be supported; and the respectivepairs of the bars are joined to each other with a band going around thehalf-circumference of the respective lower appendage (below joint) orthe upper appendage (above the joint).

The upright bars have traditionally been made from metals, such as steeland aluminum, due to their excellent mechanical strength and modulus,and also due to their ability to be shaped without breaking, whichallows the bar to be shaped to fit the patient's appendage. The fittingof a metallic bar to the patient's appendage or to the model cast of theappendage is done by mechanically bending and hammering the metal intoshape through trial and error until a desired shape is achieved. Despitecare and diligence it is difficult to obtain a completely preciseconformance of the bar to the desired shape of the patient's appendagedue to the very nature of the bending process, which is long andtedious, relying heavily on the craftsmanship of the technician. When apost-adjustment of the brace is necessary, the process of bending thebar or bars while on the brace is difficult if not impossible.

While the high strength and modulus of the metal provides the bar withexcellent performance in being able to withstand high stress and impactloads sustained during usage of a brace, the high specific gravity ofthe metals makes the brace heavy and therefore uncomfortable to wear.Moreover, many patients requiring a joint orthoses concomitantly haveweakened muscles. As such, carrying a heavy brace on the patient'sappendage has the effect of contradicting the original intention of thebrace--minimizing loads and supporting the weakened appendage and joint.

As an alternative to metal, orthosis brace bars could be fabricated fromlightweight composite materials. Fiber reinforced plastic compositeshave traditionally been made from thermoset resins such as epoxy andpolyester. The basic technique involves saturating the fibers or fabricwith a liquid resin and then curing or cross-linking the resin to hardenit. The cured finished thermoset composite cannot be reheated, softenedand shaped.

Attempts have also been made to produce a bar with a partially curedthermoset composite, so that a flat laminate bar could be formed in itssoften state, and then shaped. This is a cumbersome process requiringsophisticated, expensive machinery. Moreover, even with this machinery,the results are mixed. Because the bar cannot be resoftened after thefinal curing, post adjustment of the bar is impossible. For mostpatients, post-fitting adjustment of the brace is necessary.

While bars made with thermoplastic resin do provide repeatedthermoshaping capability, they do not have the required mechanicalperformance. This is particularly true due to the low flexural strengthand low flexural modulus of bars made solely with thermoplastic resin.The desired mechanical performance, however, could be obtained by usinghigh strength and high modulus fibers such as carbon, glass or quartzfibers. Combining these fibers with suitable thermoplastic resin couldprovide a composite with desired mechanical properties and thermoshapingcapabilities. Attempts have been made at making the upright bar usingshort fibers or discontinuous fibers by pultrusion, injection molding orcompression molding. However, discontinuities in the fiber lengthnaturally induce weaknesses in the bar, because the strength of the barstructure becomes critically weakened at the fiber lengthdiscontinuities.

Although thermoplastic composites do allow for repeated readjustments,in the application of a composite fiber layer laminate, the heating andshaping results in several problems. The dimensions of the barsgenerally used for orthosis braces are usually in the range of 16 mm×4mm (width×thickness), 18 mm×5 mm, and 22 mm×6 mm. The ratio of width tothickness typically is 3:1 to 4:1, or alternatively, the bar thicknessis approximately 25% to 30% of the width. These dimensions for acomposite laminate bar raise several problems relating to the process ofheating and shaping the bar.

For example, when the bar is heated, e.g., in an oven, to the meltingpoint of the resin and formed into a shape with a moderate 50 mm radiuscurvature, several undesirable effects occur to the bar. First, thecomposite has a tendency to loft, i.e., increase in thickness, due torelaxation of stresses in the compressed laminate. The layers may tendto separate and the overall bar shape generally distorts, that is, itdoes not remain flat and maintain a rectangular shape.

In order to "reconsolidate," the softened bar into the flat, rectangularshape and recompress the lofted composite layers, uniform pressure needsto be applied to the bar in a controlled way. This is extremelydifficult to do. It is found that when a heated bar is shaped with anykind of pressure, the pressure is unevenly imparted to the bar, causingthe bar layers to slide and lose the desired rectangular shape. Whenpressure is applied to recompress the lofted bar, local distortion ofthe bar often occurs because the pressure is uneven. Accordingly,reconsolidation leads to deformed and unacceptable bars.

Another phenomenon complicating the shaping process is the physicaldifference in the length of the top surface and bottom surface of a barshaped into an arc, as shown in FIG. 11(b). The bottom surface naturallyis shorter in length than the top surface. However, because thefiber-containing layers cannot alter in length, the bottom surfaceeither wrinkles and buckles, or the fiber-containing layers slide in thelongitudinal direction in relation to each other as shown in FIG. 12(a)through FIG. 12(b).

In practice, wrinkling or buckling is unacceptable because such a resultevidences a damaged product and is a weakness in the composite.Therefore, the sliding of the layers should be facilitated. However, inthe shaping of a composite bar, the uncontrolled sliding of thefiber-containing layers results in disorientation of thefiber-containing layers.

The net result of the above described phenomena is that the shaped barlooses as much as 50% to 80% of its mechanical strength, in addition tohaving unacceptable aesthetic appearance for use as a brace.

Attempts have been made to control the shaping process by partiallymelting the resin, so that the shape does not distort easily. While thismay result in a "good looking" bar, the strength of the bar is markedlyreduced because the sliding of the layers is effectively prevented bysome "unmelted resin." Moreover, cracks sometimes result in the barlaminate.

The prior art has also attempted the use of heat shrink tubing tocontain the body of the bar. This results in an oval shaped bar becausethe tubing tends to shrink around the bar with concentric pressure.Moreover, the commonly available heat shrink tubing is soft at themelting temperature of the bar. The pliability of this softened tubingallows uncontrolled distortion of the bar during the shaping process.

Accordingly, there appears to be a need for a lightweight thermoplasticcomposite laminate bar with high modulus and flexural strength, that isrepeatedly thermoshapable for use as the structural components inorthosis braces. There is also a need for a simple method ofthermoshaping the composite bar that maintains the high modulus andflexural strength, and the aesthetic appearance of the unshaped bar.

SUMMARY OF THE INVENTION

A thermoplastic orthopedic brace, with thermoshapable bars and an easymethod of shaping the bars as integral components in the brace areprovided by this invention. The composite bars contain multiplefiber-containing layers oriented in at least two directions related tothe bar length to provide high flexural and torsional strength. Thenovel method of thermoshaping the composite bars maintains thestructural and mechanical properties, as well as the aestheticappearance of the preshaped composite bar.

The thermoplastic orthopedic brace of this invention has the primaryattributes of being lightweight, yet having the high mechanical strengthrequired of a brace. The mechanical strength of the brace components,and therefor the strength of the brace itself, results from properselection of fiber types and resins comprising the composite. Formaximum strength, the fiber-containing layer, in all orientations, mustcontinuously extend from one edge of the bar to the opposite edge. Withthese features, this invention overcomes the problems cited above withrespect to heavy, metal orthopedic braces.

An orthopedic brace embodiment of this invention could be constructedusing upright support bars connected to each other by shapedthermoplastic composite bars to form cradle structures. Two such cradlestructures joined to each other by a mechanical joint may be held on thedistal and medial portions of a person's appendage by retaining straps.

The method of shaping the composite bars for use as the structuralcomponents in the brace solves the above described problem of inabilityto readjust the brace after an initial fitting on the patient. Throughthis method, an easy way to fit an orthopedic brace to a patient'sappendage is available.

With the invention method, thermoplastic composite bars can be easilyshaped while retaining the pre-shaped structural properties andaesthetic appearance of the bar. The method relies on two components toform a mold used to retain the structure and mechanical properties ofthe pre-shaped bar. The two components are a pair of molding stripsbetween which the composite bar is placed, and a taping means fortightly holding the molding strips in contact with the composite bar.The molding strips and taping means mold and maintain the rectangularshape and structural integrity of the thermoplastic composite bar duringheating and shaping while allowing the fiber-containing layers to slidein relation to each other. This ability for the fiber-containing layersto slide during the shaping process prevents wrinkling and buckling ofthe layers that characterize defects in the bar.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate preferred embodiments of theinvention so far devised for the practical application of the principlesthereof, and in which:

FIG. 1: is a front perspective view of a preferred unidirectional fiberreinforced thermoplastic composite tape of this invention;

FIG. 2: is a front perspective view of a composite sheet composed of aplurality of the composite tapes of FIG. 1 which have been seamedtogether along their longitudinal sides;

FIG. 3: is a top perspective view of an alternative composite sheetillustrating a plurality of composite tapes of FIG. 1 woven to form afabric;

FIG. 4: is a top planar view of a reinforcing scrim;

FIG. 5: is a top planar view of a printed fabric;

FIG. 6: is a top perspective view of a preferred polymer matrixcomposite of this invention including a laminated, thermoplasticcomposite core and a pair of fabric facing layers; and

FIG. 7(a)-(d): diagrammatically illustrate a preferred thermoformingsequence for preparing molded articles pursuant to this invention.

FIG. 8: is a side planar view of a knee orthopedic brace usingthermoplastic composite bars of this invention as the structuralcomponents of the brace;

FIG. 9: is a front perspective view of one preferred fiber orientationof the fiber-containing layers within the composite bar;

FIG. 10: is a front planar view of the preferred continuous length ofthe fiber-containing layers within the composite bar;

FIG. 11(a)-11(b): are side views of a composite bar illustrating theshaping of the bar where the fiber-containing layer lengths change asthe bar is shaped;

FIG. 12-12(b): are side views of a composite bar illustrating thedifferent results of shaping the composite bar where (a) thefiber-containing layer lengths do not change--the bottom layers wrinkle,and (b) the fiber-containing layers slide with respect to each other;

FIG. 13: is a side perspective view of the preferred sandwiching of thecomposite bar between molding strips for thermoshaping the compositebar;

FIG. 14: is a side perspective view of a thermoplastic composite barprior to thermoshaping;

FIG. 15: is a side perspective view of a thermoplastic composite barsandwiched between the two molding strips;

FIG. 16: is a side perspective view of a thermoplastic composite barprepared within the invention method for thermoshaping;

FIG. 17: is a side perspective blow-up view of a composite molding stripshowing the preferred orientation of fiber-containing layers within themolding strip;

FIG. 18: is a side perspective view of a consolidated composite laminatemolding strip.

DETAILED DESCRIPTION OF THE INVENTION Fabric-Faced ThermoplasticComposite Panel

Polymer matrix composites are provided by this invention which containfabric facing layers disposed on thermoplastic composite cores. Thesecomposite materials can be thermoformed to provide a smooth fabricsurface which is virtually free of wrinkles, kinking, and buckling. Asused herein, the term "thermoplastic" refers to any polymer resinousmaterial or blend that softens upon heating and solidifies upon coolingand can be thermoformed by application of heat and pressure. The term"fabric layer" is a relatively broad term meant to encompass both wovenand nonwoven fabric layers and scrims. Finally, the term "elasticity"means the ability of a material to distort elastically as result of theconstruction of the material or due the inherent tensile elongationproperties of the plastic or fibers used in the material.

With reference to the Figures, and particularly to FIGS. 1-3 and 6thereof, the thermoplastic composite core of this invention will now bedescribed. The thermoplastic composite core includes a thermoplasticmatrix containing a reinforcement, preferably reinforcing fibers, andalso singular layers of thermoplastics sandwiched in the composite core.

The thermoplastic matrix of the composite cores of this inventioncontain one or more thermoplastic resins, alloys or copolymers. Typicalresins useful in this regard include acetal, acrylics, cellulosics,fluorocarbons, nylons, polyallomer, polyaryl ether, polyaryl sulphone,polycarbonate, polyethylenes, polyimide, polyphenylene sulfide,polypropylene, polystryrene, polyurethane, polyvinyl chlorides, styreneacrylonitrile, polyphenylene oxide, polysulfone, polyether sulfone,polymethylmetha acrylates, polyesters (PET, PBT), and their respectivecopolymers, compounds, and derivatives.

The preferred reinforcing fibers 12 of this invention are of thelight-weight and high-strength high modulus variety, such as carbon,glass, aramid, metal, or ceramic fibers. These fibers are preferablyuniformly distributed throughout the composite to about 10-80 vol. %,and preferably at least about 30% volume. Factors that influence thefatigue resistance and tensile properties of reinforced thermoplasticsinclude the proportion of reinforcing fibers, morphology of thereinforcement (i.e. random chopped mat, unidirectional fiber, or wovencross-ply roving), and the matrix resin. For example, incarbon-reinforced composites, fatigue, and tensile performance ofchopped-mat reinforcement is significantly lower than that of a woven,cross-ply fabric.

Advanced composites, such as unidirectional carbon/thermoplasticlaminates can have better fatigue resistance than steel, aluminum, orglass-reinforced composites. Compared with unidirectional laminates, thefatigue strengths of other reinforcement types in decreasing order are:85% unidirectional, cross-ply, glass fabric, and randomly oriented shortfibers. Accordingly, this invention prefers that the fibers areunidirectional and that the composite material contain a laminatedstructure. Discontinuous fibers more closely model the fatigue strengthof the polymer matrix, making fiber-to-matrix bonding more important foroptimum performance.

Presently, the preferred fibers of this invention comprise carbon,glass, such as E-glass and S-glass, boron, aramid, such as KEVLAR® 29 orKEVLAR® 49 (available from du Pont), ceramic fibers, metallic fibers,and metal coated fibers.

The above-described thermoplastic resins and reinforcing fibers can bearranged in a number of variations to produce dozens ofthermoplastic-fiber composites. Some of these variations are described,along with their resulting fatigue properties, in Table I below:

                  TABLE I                                                         ______________________________________                                        Fatigue Strength of Reinforced Thermoplastics.sup.1                           Material    Glass    Carbon   Strength, × 10.sup.3 psi                  cycles      fibers, %                                                                              fibers, %                                                                              @ 10.sup.4 cycles                                                                     @ 10.sup.7                              ______________________________________                                        Acetal Copolymer                                                                          30       --       9       7                                       Nylon 6.sup.2                                                                             30       --       7       5.7                                     Nylon 6/6   --       --       6       5                                       Nylon 6/6.sup.2                                                                           --       --       3.4     3                                       Nylon 6/6.sup.2                                                                           30       --       8       6                                       Nylon 6/6.sup.2                                                                           40       --       9       7                                       Nylon 6/6   40       --       10.5    9                                       Nylon 6/6.sup.2                                                                           --       30       13      8                                       Nylon 6/6.sup.2                                                                           --       40       15      8.5                                     Nylon 6/10.sup.2                                                                          30       --       7       5.5                                     Nylon 6/10.sup.2                                                                          40       --       8       7                                       Polycarbonate                                                                             20       --       9       5                                       Polycarbonate                                                                             40       --       14.5    6                                       Polyester, PBT                                                                            30       --       11      5                                       Polyester, PBT                                                                            --       30       13      6.5                                     Polyetheretherketone                                                                      --       30       18      17.5                                    Polyethersulfone                                                                          30       --       16      5                                       Polyethersulfone                                                                          40       --       19      6                                       Polyethersulfone                                                                          --       30       22      6.7                                     Mod. Polyphenylene                                                                        30       --       7       4.7                                     Oxide                                                                         Polyphenylene                                                                             --       30       13      9.5                                     Sulfide                                                                       Polysulfone 30       --       14      4.5                                     Polysulfone 40       --       16      5.5                                     ______________________________________                                         .sup.1 Tests by ASTM D 671 at 1,800 cycles/min., as reported in Advanced      Materials & Processes, Vol. 137, Issue 6, p. 102 (June 1990).                 .sup.2 Moisture conditioned, 50% R.H.                                    

The thermoplastic composite core of this invention can be fabricated ina number of ways. One method is to begin with continuous rovings orbundles of fibers. The rovings are spread out to separate the filamentsand then they are passed through a fluidized bed of thermoplastic resinpowder. The spread fibers pick up the powder as they pass through thefluidized bed. The now resin-coated fibers are heated to the meltingpoint of the thermoplastic resin in an oven to smoothly coat the fibersto wet them out completely, or as nearly completely as the processpermits. Since the now-coated fiber bundle is in a nongeometric shape,it is then passed through a die or former to shape the bundle into atape-like configuration. This tape preferably has a width which is muchgreater than its thickness. The thickness should be at least 50 μm so asto have sufficient strength to withstand mechanical working into thefinal thermoplastic matrix, and a preferred width of at least about 3 mmto avoid over twisting during the subsequent mechanical operations.

Alternatively, the fibers may be passed through an extrusion cross-headdie containing a bath of molten thermoplastic polymer. As the fiberspass through the die, the molten polymer coats the fibers and completelywets them out. This operation could also be followed by a shaping stepto configure the coated bundle of fibers into a tape configuration.Other methods include passing the fibers through a solution in which thepolymer powder is suspended, or sandwiching the fiber web between filmsof polymer, and then passing them through heated laminated rollers underpressure and elevated temperature to coat them. Both of thesefabrication methods can be additionally followed by a forming step toproduce tapes.

The end result of these impregnation methods is that a tape 10 is formedin which there are continuous unidirectional fibers 12 in the axial orlongitudinal direction, and that these fibers 12 are encapsulated withina thermoplastic, thermoformable matrix 14, as substantially described inFIG. 1.

In order to produce a panel from these unidirectional fiber reinforcedthermoplastic tapes 10, a plurality of tapes can be woven into sheetfabric, such as woven sheet of tape 30, shown in FIG. 3. In this wovensheet 30, the tapes 10 are oriented in the 0° and 90° direction. Suchwoven constructions are disclosed in U.S. Pat. No. 5,082,701, which ishereby incorporated by reference. Alternatively, the tapes can be placedadjacent to one another and seamed, attached, welded, or stitched inposition before laying the next tape 10 as shown by seamed sheet 20 ofFIG. 2.

In an alternative procedure for constructing panels, a "commingled fiberfabric" is produced. Fibers or thermoplastic resin and reinforcingfibers are commingled into a yarn. The commingled yarns are then woveninto fabric. The fabric or layers of fabric are compression molded intoa flat laminate under heat and pressure. The resin fibers melt and flowto wet out the reinforcing fibers.

In still another method, an "assembled composite" can be produced. Insuch a method, woven or nonwoven fabric random or directional webs ofreinforcing fibers are alternately stacked with a layer of thermoplasticfilm or powder. This assembly is then consolidated into a laminate underheat and pressure. Also, the method described by Fitchmun, U.S. Pat. No.4,778,717 whereby a fabric is dipped in a liquid resin may be employed.

Referring to the polymer matrix composite material 100, shown in FIG. 6,it will be understood that the preferred thermoplastic composite core isproduced by laminating at least two thermoplastic sheets comprisingunidirectional fibers having different orientations. These sheets aredesirably placed on top of one another; for instance in a 0°/90°/0°/90°orientation that would be functional. However, it will be understoodthat there are numerous orientations and ply combinations.

The sheets used in the thermoplastic composite core in this embodimentcan be thermoformed to laminate them together into a integral composite.In one manufacturing sequence, the laid up sheets are placed in acompression molding press, where heat and pressure are used toconsolidate the assembled sheets into a nearly void-free solid compositelaminated panel. It is envisioned that both seamed sheets 20 and wovensheets 30 can be used interchangeably in the laminated construction.Alternatively, commingled fibers fabric or the assembled composite(described above) can be incorporated into the structure of thelaminated composite panels.

Additionally, a thin thermoplastic film can be placed on both sides ofthe laminated composite, particularly if the top laminated sheetscontain woven tapes, to fill in any voids resulting in the lamination ofthe woven pattern. The polymeric ingredients disclosed for the matrix ofthe thermoplastic composite core would be suitable resins for this film.

The preferred fabric layer 40 of this invention will now be described.Although woven and nonwoven fabrics and scrims are suitable for thisinvention, woven fabrics are the most desirable. A fabric 40, such asthat described in FIG. 4, is a nonwoven fabric, screen of bonded fibersor a woven fabric, whereby the construction permits the yarns orindividual fibers to move relative to their intersection points.

The fabric layer of this invention does not necessarily need tocontribute to the mechanical properties of the panel, therefore it doesnot have to, but may, contain high strength fibers, such as those typesof fibers reinforcing the thermoplastic composite core. Instead ofcarbon, glass, or aramid fiber, the fabric layer 40 of this inventionpreferably contains ordinary, natural, or synthetic fibers, such ascotton, wool, silk, rayon, nylon, polyester, polypropylene,polyethylene, etc. The advantage of using these traditional textilefibers, is that they are available in many colors and can provide aninfinite variety of patterns and textures to the preferred fabriclayers. Such fibers can be woven, or spunbonded to produce nonwoventextile fabrics. Alternatively, plain color fabric can be easily dyedand printed in a variety of colors and patterns. Additionally,reinforcing fibers, such as glass, carbon, and aramid, could be used forsurface fabric, provided the overall fabric construction allowssufficient elasticity.

As described in FIG. 5, the preferred woven fabric 50 can include aprinted, aesthetically appealing printed pattern. The pattern can becreated by weaving different colored fibers into an ornamental design,however, this would involve using numerous yarn inputs with differentcolors in the warp, and complex weft inputs to obtain sophisticatedpatterns. A less expensive alternative would be to use commerciallyavailable patterned fabrics, which are intended for garments orfurniture, etc., and apply these fabrics to the thermoplastic compositecore of this invention. Accordingly, this invention prefers to employconsumer textile fabrics, imprinted with art work, logos, and trademarkswhich are printed, dyed, or silk screened onto the fabric.

The fabric layers of this invention are preferably bonded to theresin-containing thermoplastic composite core with a "resinousadhesive", e.g. film, powder, or tacky material used to bond the fabricto the core. One preferred method of applying the fabric layer to thecore is to prepare a thin film, 10 μm to 500 μm thick, made from acompatible thermoplastic resin as the matrix of the thermoplasticcomposite core. This film can be placed over the core and the fabriclayer is then placed onto this film. Another film of the same or similarcomposition is preferably applied to the top of the fabric. The assemblyincluding the core, fabric layer, and the layers of thermoplastic filmis then placed into a compression molding press which subjects thecomponents to elevated heat and pressure. The films, fabric, and coreare thereafter consolidated and fused into an integral panel shape. Thetotal amount of film needed to fully bond, incorporate, and/or cover thefabric depends upon the thickness, porosity, and texture or the fabric.As a rule of thumb, the total film thickness should be about 0.3 toabout 3.0 times the thickness of the fabric. One may use more film belowor above the fabric to impart aesthetic appearances, e.g., texture,depth, etc.

In the most preferred construction, the fabric layer weave and the fiberconstruction of the core are chosen so that the melted film resin flowsthrough the interstices in the fabric layer weaving to anchor the fabricto the panel. Additionally, the fibers of the fabric layer can beintertwined and bonded closely with the fibers of the core to increasethe adhesion of the fabric layer to the core. It is further envisionedthat the thermoplastic film can be substituted by an evenly distributedresin powder or a suitable adhesive to achieve the same result. Thefabric, thus applied to one or both planar surfaces of the panel-likecore, becomes the outermost layer of the composite material, and acts toovercome the problems of wrinkling, and a lack of an aestheticappearance usually associated with conventional composite materials.

The polymer matrix composite materials of this invention arethermoformable, and can be used to produce molded articles ranging fromsuitcases to shoe supports. Referring to FIG. 7, a thermoforming methodfor producing a safety shoe toe protector is diagrammatically described.The composite material is heated in step 7(a), followed by placing theheated material onto a mold in step 7(b). Under heat and pressure, forexample using vacuum forming or compression molding, the mold conformsthe heated composite material to a given shape in step 7(c). In step7(d), the die is opened, and the finished, thermoformed part--in thiscase, a safety shoe toe protector--is removed and cooled.

From the foregoing, it will be understood that this invention providespolymer matrix composites having a bonded fabric layer which can bethermoformed without wrinkling or distortion. The difference in theelasticity between the fabric layer and the thermoplastic composite coreof this invention is sufficient so that when the mold is applied tothermoform the composite material, the fabric layer stretches to conformsmoothly to the core over contours and the like. Although variousembodiments have been illustrated, this was for the purpose ofdescribing, and not limiting the invention. Various modifications willbecome apparent to one skilled in the art, and are considered within thescope of the attached claims.

Thermoplastic Orthopedic Brace and Method of Manufacturing Same

A lightweight orthopedic brace constructed from thermoshapable,thermoplastic composite laminate bars is provided by this invention. Anovel method for easily shaping the bars that maintains the mechanicaland structural integrity of the pre-shaped composite bars is alsoprovided. The materials and processes described above for the compositepanel embodiment are hereby incorporated by reference.

The terms "thermoplastic" and "fabric layer" are as defined above. Theterm "fiber-containing layer" is similar to fabric layer in that itmeans the layers used to build up a composite laminate within whichfibers are contained. The terms "thermoshaping" or "thermoshapable" meanthe ability or action of shaping an object that softens upon heating andresolidifies after cooling.

With reference to the Figures, the orthopedic brace embodiment of thisinvention is described in the following text. As illustrated in FIG. 8,an orthopedic brace 200 is constructed from a pair of upright bars 202connected to a series of bands 201 which extend around the halfcircumference of the patient's upper or lower appendage. These uprightbar/band structures are connected to a hinge mechanism 203 that iscentered at the patient's joint to be supported, such as a person'sknee, shown in FIG. 8. Flexible bands 204 are attached to the uprightbars 202 to hold the brace on the patient's appendage. In a preferredembodiment, an orthotic support 205 can be attached to the braceproviding support for the patient's hand or foot.

There clearly is a vast range of demands placed upon an orthopedicbrace. For example, a child with a slightly injured elbow or knee wouldplace minimal stress on the brace, while a heavy set young athlete witha dislocated knee would put severe demands on the brace and itsmaterials. In this invention the orthopedic brace upright bars 202 andbands 201 are constructed from thermoplastic composite laminates.

The upright bar 202 is fabricated from a thermoplastic compositelaminate containing multi-axial fiber orientation, with a substantialnumber of fibers along the bar 202 length. The fibers are impregnatedwith a suitable thermoplastic resin and consolidated into a compositelaminate.

In order to withstand the dynamic and static stresses and strainstypically found in an arm or leg brace, the fibers must havesufficiently high tensile and flexural strength and modulusrespectively. The quantitative values desirable in the fiber are asfollows:

    ______________________________________                                                        Minimum   Preferred                                           ______________________________________                                        Tensile Strength (MPa)                                                                          2500        3500                                            Tensile Modulus (GPa)                                                                           60          200                                             Specific Tensile  1.0         2.0                                             Strength* (10.sup.7 cm)                                                       Specific Tensile  0.23        1.0                                             Modulus** (10.sup.9 cm)                                                       ______________________________________                                         *Specific Tensile Strength = Tensile Strength/Density                         **Specific Tensile Modulus = Tensile Modulus/Density                     

The type of fibers that could meet these described requirements includemetal, carbon, glass, quartz and ceramic. While the aramid fibers meetthe tensile requirement, they are less desirable since they tend to nothave sufficient flexural properties to provide sufficient rigidity tothe bar. As such, the aramid fiber is not the preferred primary fibercomponent of the bar. While a functional bar containing glass fiberscould be made for a low demanding application with the minimumproperties, the preferred properties are desirable for mostapplications.

For comparative purposes, the mechanical properties of metals and twotypes of fibers as used in thermoplastic bars are provided in thefollowing table.

    ______________________________________                                                                           Low                                                                           Modulus                                              Aluminum                                                                              Steel   Carbon   E-Glass                                    ______________________________________                                        Tensile (MPa)                                                                             275       1000    4100   3450                                     Strength                                                                      Tensile     68        207     227    72                                       Modulus (GPa)                                                                 Density (g/cm.sup.3)                                                                      2.7       7.9     1.8    2.58                                     Specific    0.10      0.12    2.27   1.33                                     Tensile                                                                       Strength (10.sup.7 cm)                                                        Specific    0.25      0.26    1.26   0.28                                     Tensile                                                                       Modulus (10.sup.9 cm)                                                         ______________________________________                                    

The preferred fiber layers for the bars are carbon fibers, followed byglass fibers. This is because the high physical strength properties andextremely low specific gravity of the carbon fiber make the bar a verylight weight and very strong brace component. While the low moduluscarbon and E-Glass are stated in the above property table, other gradesof carbon and glass can also be used.

Selection of the fiber-containing layer involves a balance between theexpense of the components and the required performance of the compositestructure system. Although the carbon fiber has been found to offer thebest specific tensile strength and modulus, it is also possible toincorporate other fiber types in the laminate for various purposes,e.g., glass fiber to reduce the cost, or aramid fiber to alter thefailure mode characteristics.

Since thermoshaping is a key element of the invention, the resin type tobe selected is desirably a thermoplastic material. The thermoplasticresin should have sufficient mechanical properties to impart strength tothe final composite laminate. For example, a softer resin, e.g.,ethylene vinyl acetate or low density polyethylene, would make a weakcomposite which would be less desirable for the demanding requirementsof a knee brace.

It has been found that the following properties of the resins arepreferable to produce a bar with functional characteristics. Minimum andpreferred property values are shown.

    ______________________________________                                                      Approximate                                                                   Minimum    Preferred                                                          Values     Values                                               ______________________________________                                        Tensile Strength (MPa)                                                                        25.00        60                                               Tensile Modulus (GPa)                                                                         1.200        2.0                                              Flexural Modulus (GPa)                                                                        1.200        2.0                                              ______________________________________                                    

The resins that meet the minimal values include polypropylene, highdensity polyethylene, polyamide 12, certain polyurethanes and polyestersand their respective copolymers and derivatives. The preferred resinshave been found to have generally high tensile and flexural modulus.These resins include polyamides such as Nylon 6, and Nylon 6,6,polymethyl metha acrylate (acrylic resins), polycarbonate, polyethyleneterphathalate, polybutylene terphathalate, polyphenylene sulphide, highhardness polyurethanes, and their copolymers and derivatives. Theselisted resins only are given as examples. The invention is not meant tobe restricted to named resins only.

The preferred resins were found to be Nylon 6 and polymethylmethacrylate in order to achieve high flexural modulus, while having amoderate melting point below 250° C. While resins such aspolyphenylene-sulphide and polyetherimide provide very high mechanicalproperties, their melting points are over 275° C. Composites made withthese resins would require special high temperature ovens that would notcommonly be available to the general small orthopedic workshops.

As previously discussed, the primary property required of the uprightbar is high flexural strength and modulus. This is best achieved throughcontinuous fiber lengths orientated in the upright composite bar 300longitudinal or 0 degree direction, as shown in FIG. 9 and FIG. 10. Asecondary property required of the upright bar is the need for hightorsional resistance. Torsional strength is best achieved throughorientation of a portion of the fibers in the 45 degree direction andpossibly in the 90 degree direction, as illustrated in FIG. 9.

It has been found that in order to obtain the best functionalperformance in the bar, in terms of flexural properties, about 30% to95% of the fibers can be oriented in the 0 degree direction, andpreferably about 45% to 75% of the fibers in the 0 direction. Thehighest torsional resistance has been found to be achieved by havingabout 5% to 65% of the fibers in the 45 degree direction and preferablyabout 15% to 50% in the 45 degree direction. The fibers described asbeing oriented at 45 degrees may equally be in the 1 degree to 90 degreerange. For example, some fibers may be oriented at about 30 degrees,some at about 45 degrees, and some at about 90 degrees. The objective isto have fibers in the non-zero direction to resist twisting forcesimparted to the bar.

The length of the fibers in the bar is important, in that the criticalfactor is that the fiber layer within the bar must be substantiallycontinuous. While attempts have been made to produce bars with long butdiscontinuous fibers, these systems result in very inefficientcomposites. Because the mechanical performance of the bar ispredominantly obtained from the fibers, discontinuities or gaps in thefiber lengths results in lower mechanical properties.

Accordingly, the most preferred fibers, regardless of orientation, havea continuity from one edge of the bar to the opposite edge of the bar,as shown in FIG. 10. For example, the fibers in the 0 degree orientationwould desirably extend from the lower end of the bar to upper end, whilethe fibers in the 45 degree orientation would extend from one side tothe other side of the bar, as provided in FIG. 10.

As has been discussed earlier, the composite derives most of itsmechanical properties from the fiber rather than the resin. It istherefore desirable to use a high volume content of fiber. A limitationto the volume of fiber layers is that there must be sufficient resincontent to ensure uniform coating and wet-out of the fibers to provideintegrity to the composite body. It has been found that the fiber volumecontent preferably is about in the 25% to 75% range to be of functionaluse in the bar. The preferred fiber volume content range was found to beabout 30% to 55%.

The principle of the composite laminate fabrication is that the resinimpregnated fibers are stacked in a multi-layer structure, with thefiber directions in each layer appropriately oriented. The structure isthen consolidated under heat and pressure into a laminate. The laminatebar described by the present invention could be in the form ofindividual bars formed in a mold, or made from a large panel from whichindividual bars are subsequently cut.

The ideal method for shaping the composite laminate bar of thisinvention would include (1) permitting the bar to maintain a flat andrectangular shape during heating without lofting, (2) handling the barhandled with gloved hands, (3) placing the bar on the plaster cast of aleg, and (4) pressing down with reasonable hand pressure to a desiredshape. The resulting shaped bar would maintain its original integrity,including its rectangular profile and mechanical properties. The novelinvention method described herein practically achieves all the elementsof the ideal method described above.

The preferred inventive method involves two physical components attachedto the composite bar 300 prior to placing it in the oven. Thesecomponents act as a mold to maintain the rectangular shape of the bar300 during the heating and shaping process.

Reference is now made to FIG. 13. The preferred molding strip 320, is athin material in which its plane can be bent or flexed in the A-Bdirection (up or down). The molding strip 320 preferably does not bendin the A-C direction, or stretch in the A-D direction and mostimportantly, the molding strip 320 should not be compressed in the shownX-Y direction.

Two molding strips 320 can be placed on the wider sides of the bar 300,as shown in FIG. 14 and FIG. 15, to further control the molding process.When the bar is bent and shaped in the A-B direction, the molding strips320 would bend with it.

A high temperature tape 330, with or without adhesive, can be spirallywrapped around the bar/strips sandwich, as illustrated in FIG. 16. Thetape provides a jacket around the sandwich formed by the bar 300 andstrips 320; holds the strips 320 in an intimate contact with the bar300; and prevents sideways movement of the softened bar 300 (i.e., inthe A-C direction shown in FIG. 13). Although heat shrink tubing couldbe used in place of the tape 330, it has been found to be lesseffective.

The resulting assembly of composite bar 300, molding strips 320 and tape330 is a novel "mold" formed around the bar 300 to maintain the barshape. The strips 320 maintain a smooth flat surface of the bar 300 atall times and allow controlled bending and shaping of the bar 300 in theA-B direction. It is important to note that because the strips 320 aredesirably not capable of being compressed in the X-Y direction, theintegrity of the bar shape is contained within the edges of the twostrips 320.

A key property of the tape 330 is that at the shaping temperature itshould not become soft and pliable. In a preferred embodiment, twolayers of high temperature tape 330 should be tightly wrapped in aspiral fashion around the composite bar 300 held between the two moldingstrips 320. Each layer of the tape 330 is preferably disposed at crossangles to maintain the stability of the assembly. Where only one spirallayer of the tape 330 is used, the bar 300 may become slightly twisted.

Because the tape does not soften or stretch during the heating process,the bar is not allowed to loft. Accordingly, the original dimensions ofthe bar between the strips are maintained. Also because the tape isessentially nonstretchable, the body of the bar is prevented fromsliding sideways in the A-C direction even when pressure is applied toshape the composite bar.

This simple method also facilitates the sliding of fiber layers in thelongitudinal direction, i.e., A-D direction as shown in FIG. 13, withoutcausing distortion of the bar. The ends of the bars are preferably open,and during bending, the fiber layers are free to slide within therectangular mold (formed by strips and tape) in the A-D direction, sothat no wrinkling or buckling occurs at the bottom surface of the bar,as shown in FIG. 12-12(b).

A further advantage of this inventive method is in the relativeinsensitivity of the thermoshaping process to molding temperature.Without use of the inventive method mold, if the heating time was tooshort or the temperature was too low, the bar would tend to wrinkle ordelaminate during the shaping process. Alternatively, if the heatingtime was too long or the temperature was too high, the bar would tend tolose its shape and become unacceptably deformed. By contrast, with theuse of the strip/tape assembly method, the bar can be heated to atemperature slightly more than necessary to ensure thorough melting ofthe resin, and the bar will still maintain its integrity and shape.

The molding strip 320 can be constructed from metal or plastic. However,its melting or softening temperature should exceed that of the resin thecomposite bar. For a composite molding strip, the resin could bethermoset, such as epoxy or polyester. For a composite thermoplasticstrip, the resin could be Nylon 6 or polyphylene sulphide. For thetypical upright bar dimensions, as used for orthopedic braces, thepreferred dimensions of the strip should be within the range of about0.1-2.0 mm.

In a preferred embodiment, the molding strip 320 could have a similarcoefficient of expansion as the composite bar 300, particularly alongthe bar length. This can be achieved, in part, by using fibers in themolding strip 320 which are similar to those used in the composite bar300. A composite molding strip made of carbon, glass, ceramic or quartzfibers with a suitable temperature insensitive resin is found to be thepreferred embodiment.

For the preferred composite molding strip 320, the preferred fiberorientation is 90 degrees (i.e., A-C direction, as shown in FIG. 18).Alternatively, the majority of fibers could be oriented in the 90degrees direction with less than 50% fibers at 0 degrees (i.e., A-Ddirection, shown in FIG. 18) to ensure some integrity to the strip, asshown in fiber layers 311 of FIG. 17. The fibers oriented at 90 degreeswould prevent the compression of the strip in the X-Y direction and yetallow bending in the A-B direction. These fibers could be encapsulatedby a suitable resin. The strip could also be made from woven fabric ofthe fibers and impregnated with suitable resin.

The tape 330 can be a thermoplastic tape, such as polyester, as long asits softening temperature is significantly higher than the temperatureof the composite bar to be shaped. A polyester tape with softeningtemperature of about 250° C. works well on a composite bar made withNylon 6 with a softening temperature of about 220° C. The tape 330should be substantially nonstretchable and nonpliable at the softeningtemperature of the composite resin. Such tape materials may includepolymerics, polymerics with reinforced fibers that are "non-stretching",e.g., glass, cotton, or tape made from fibers such as glass, cotton orpolyester.

For composite bar dimensions typically used for orthopedic braces, thetape thickness should be in the range of about 0.01 mm-1.0 mm, andpreferably be about in the 0.04 mm-0.4 mm range. The ideal thicknessdepends on the type of tape material used, e.g., a very stiff polyestertape needs to be about in the 0.04 mm range, while a woven glass fibertape could be as thick as about 0.4 mm.

In a preferred embodiment, the taping means could be a heat-shrink tape.The advantage of a heat-shrink tape is that any relative looseness orsloppiness in wrapping over the sandwiched bar, is removed as the tapeshrinks tightly around the bar. However, normal non-shrink tape workswell when wrapped tightly.

In another embodiment, the taping means may have an adhesive on it. Thepresence of adhesive facilitates the wrapping process as the tape cannotbecome easily unravelled. However tape without adhesive works well, aslong as the starting and ending portions of the wrapped tape aresecurely fastened by, for example, an adhesive.

The taping means could also be in a tubular form. The tube diameter mustbe large enough to be inserted over the sandwiched composite bar. Thetube diameter could then be reduced in diameter to provide a mold overthe bar. This could be achieved by using a heat-shrinkable polymerictubing, or an appropriately knitted tube, e.g., glass, carbon or otherfiber capable of withstanding the softening temperature of the barresin.

EXAMPLE

A 450 mm long carbon/polyamide composite bar was sandwiched between twocarbon/polyphenylene sulphide molding strips. This assembly was wrapped,without adhesive, with HI-SHRINK polyester tape, 19 mm in width and 0.05mm in thickness, from Dunstone Company, Inc.

The starting and the ending portions of the above tape were secured witha high temperature adhesive tape. A first tape layer was spirallywrapped with an approximate 2.5 mm overlap at an angle of approximately+45°, and then a second layer was spirally wrapped similarly but in the-45° angle. The assembled bar was then placed in an oven at 230° C. for12 minutes until softened.

The bar was removed using gloved hands, and placed on a plaster legcast. In order to apply more uniform pressure on the bar, an aluminumstrip 50 mm wide×0.4 mm thick and 500 mm long was placed on the bar.This thin aluminum strip was pliable and flexible. Hand pressure wasapplied on the aluminum strip to force the bar assembly to conform tothe plaster cast. Slight pressure was also applied to ensure that the"compressive consolidation" of the bar was maintained particularly atthe sections with sharp bends.

The composite bar/mold assembly was maintained in this position for 2minutes, and then cooled in cold water for 3 minutes. The polyester tapeand the molding strips were removed. The resulting shaped bar retainedits original rectangular cross-section and maintained excellentconsolidation.

Tests were conducted on the bars before and after shaping with thefollowing results. For comparative purposes, the values for bars shapedwithout molding strips or tapes are also shown.

    ______________________________________                                                          Bar Shaped                                                                    Bar Shaped                                                                    With      Without                                                   Original  Invented  Invented                                                  Bar       Method    Method                                            ______________________________________                                        Flexural Break                                                                          2160        2150      1975                                          Load (N)                                                                      Flexural   669         572       387                                          Strength (MPa)                                                                Flexural   50          44        20                                           Modulus (GPa)                                                                 ______________________________________                                    

The above values plainly show the benefit of using the invention method.About 85% of the preshaped composite bar mechanical properties aremaintained using the inventive method while the bar shaped without theinventive method lost approximately 60% of its preshaped mechanicalproperties.

Accordingly, from this invention description, a lightweightthermoplastic orthopedic brace is provided along with a method of easilythermoshaping the composite laminate bars used in the orthopedic brace.This method maintains the structural and mechanical properties of thepre-shaped composite bar. Although several embodiments of the compositebar and method of manufacturing it have been illustrated, theseembodiments were for the purpose of describing and not limiting theinvention. Various modifications will become apparent to one skilled inthe art, and are considered within the scope of the attached claims.

What is claimed is:
 1. A fitted orthopedic brace component, comprising athermoplastic composite laminate bar including,a plurality offiber-containing layers impregnated with a thermoplastic resin, saidfiber-containing layers forming a composite laminate having fibersoriented in at least two directions within the bar for providing highflexural and torsional strength when consolidated under heat andpressure.
 2. A fitted orthopedic brace component of claim 1, whereinsaid fibers within the fiber-containing layers extend substantiallycontinuously from one end of the bar to the opposite end of the bar. 3.A fitted orthopedic brace component of claim 1, wherein saidfiber-containing layers are selected from the group comprising metal,carbon, glass, quartz, aramid, ceramics and mixtures thereof.
 4. Afitted orthopedic brace component of claim 1, wherein said thermoplasticresin is selected from the group comprising polyamide, polymethylmethacrylate, polycarbonate, polyethylene terphathalate, polybutyleneterphathalate, polyphenylene sulphide, polyurethane, and theirrespective copolymers, compounds and derivatives.
 5. A fitted orthopedicbrace component of claim 2, wherein about 30% to 95% of thefiber-containing layers are oriented along the length of the bar, and aportion of the remaining fiber-containing layers are oriented indirections other than along the length of the bar.
 6. A fittedorthopedic brace component of claim 2, wherein said fiber-containinglayers comprise about 25% to 75% of the laminate bar volume.
 7. A methodof shaping thermoplastic composite bars, which comprises;sandwiching thecomposite bar between a pair of molding strips; wrapping the bar andmolding strips in taping means, creating a mold assembly encasing thecomposite bar; heating the mold assembly and composite bar; shaping theheated and softened mold assembly and composite bar into the desiredcontour; cooling said shaped mold assembly and composite bar; andremoving the mold assembly from the shaped composite bar, whereby adesired curvature of said bar is rigidly retained.
 8. The method ofshaping thermoplastic composite bars of claim 7, wherein said moldingstrips have a thickness in the range of 1/50 to 1/5 the thickness ofsaid bar.
 9. The method of shaping thermoplastic composite bars of claim7, wherein said molding strips are selected from the group of materialscomprising metal, plastic, composite and derivatives thereof.
 10. Themethod of shaping thermoplastic composite bars of claim 7, wherein saidmolding strips are made of a composite with at least onefiber-containing layer selected from the group containing metal, carbon,glass, ceramic, quartz and derivatives thereof, said fiber-containinglayer being impregnated with a thermoset resin.
 11. The method ofshaping thermoplastic composite bars of claim 10, wherein saidfiber-containing layer is impregnated with a thermoplastic resin. 12.The method of shaping thermoplastic composite bars of claim 10, whereinmore than 50% of the fiber in said fiber-containing layer is orientedalong the width of the molding strip.
 13. The method of shapingthermoplastic composite bars of claim 7, wherein said taping means is aheat-shrink tape.
 14. The method of shaping thermoplastic composite barsof claim 7, wherein said taping means contains an adhesive on one sideof the tape.
 15. The method of shaping thermoplastic composite bars ofclaim 7, wherein said taping means is a tube with internal diameterreducible to tightly fit around the composite bar sandwiched between thepair of molding strips.
 16. The method of shaping thermoplasticcomposite bars of claim 15, wherein said tube is made from heat-shrinkplastic or knitted fiber.
 17. The method of shaping thermoplasticcomposite bars of claim 7, wherein said taping means has a thickness inthe range of about 1/500 to 1/5 the thickness of said composite bar. 18.The method of shaping thermoplastic composite bars of claim 7, whereinsaid taping means has a softening temperature greater than the softeningtemperature of said composite bar.
 19. The method of shapingthermoplastic composite bars of claim 7, wherein said taping meanscomprises: a first tape wrapped about the composite bar and moldingstrips in a spiral manner in a first orientation along a portion of thelength of the bar; and a second tape wrapped about the composite bar andmolding strips in a spiral manner in a second orientation along aportion of the length of the bar.
 20. A method of shaping thermoplasticcomposite bars, which comprises,sandwiching the thermoplastic compositebar between two molding strips, said molding strips having essentiallythe same width and length as said composite bar, said molding stripsfurther having a thickness in the range of about 1/50 to 1/5 of thethickness of said composite bar, said molding strips further having amelting temperature substantially higher than the composite bar;wrapping said thermoplastic bar sandwiched between the two moldingstrips with a high temperature tape, said high temperature tape having asoftening temperature higher than the composite bar, whereby saidmolding strips are held in contact with said composite bar; said moldingstrips and tape forming a mold for minimizing the expansion in thicknessor lateral deformation of the composite bar upon heating the mold andcomposite bar; heating said mold and thermoplastic composite bar tosoften the thermoplastic composite bar; shaping said softened, heatedmold and composite bar to the desired curvature; cooling said shapedmold and composite bar; and removing the high temperature tape and thetwo molding strips from the composite bar, whereby the desired curvatureof the thermoplastic composite bar is rigidly retained.